The present invention relates to sidewalk and road construction and more particularly to systems and methods for installing concrete curb, straight and curved, faced with steel to protect the concrete from damage due to cars, trucks and snow plows.
At the present time, in cities and in metropolitan areas, a sidewalk is located at a side of a road, e.g., street or roadway. The sidewalk is elevated typically 7xe2x80x3 above the road (the reveal), and a curb is used to separate the road from the sidewalk. The curb has a nearly vertical face which ranges from 18xe2x80x2 to 27xe2x80x3 depending on the thickness of the road and the reveal of the curb. The bottom of the curb is buried 11xe2x80x3 to 20xe2x80x3 below the road, and has a nearly horizontal portion which lines up with the sidewalk. There is a xc2xdxe2x80x3xc3x976xc2xdxe2x80x3xc3x9718-27xe2x80x3 premolded bituminous expansion joint filler (EJF) between curb sections and a xc2xcxe2x80x3 expansion joint between the curb and sidewalk for expansion and contraction. When the curb and sidewalk are poured simultaneously, a xc2xdxe2x80x3 thick expansion joint (EJF)is generally used between the curb and sidewalk.
Plain concrete is most often used for such curbs. In high traffic areas, such as busy city streets, the concrete is rapidly chipped, cracked and broken, so a hard stone, such as granite, is often used. However, the costs of cutting, transporting and installing elongated granite curb members is high and may be prohibitive.
Steel has been used for many years to face concrete curb since it is strong and can resist damage caused by the impact of the truck wheels and snow plows when installed along streets having heavy vehicle traffic. Steel faced concrete curb is less costly than granite but as good as, or superior, in resisting damage. However, steel curb-facing (steel curb) is heavy and, because it is heavy and clumsy to handle, it is costly to install. A typical steel curb is 20 feet long, asymmetrical, and weighs about 340 pounds. It usually requires a four-man crew to lift and install a steel curb or two men with a lifting machine. The curb, during its installation, must be exactly aligned with a string guidance line. The surfaces of adjacent steel curbs must align smoothly where they join each other. If one steel curb extends beyond or above the next, it will present a sharp edge which can cut vehicle tires and present a tripping hazard to pedestrians.
To rebuild an existing road, generally the curb to be replaced is removed. A trench, 11 to 18 inches deep and 18 to 24 inches wide, is then dug. Using surveyor instruments, including a surveyor""s level, a continuous guidance string is strung as a guide for the curbs. The string is supported by long steel (primary) stakes, for example, xc2xe-inch diameter and 36-inch long. The primary stakes are about 50 feet apart and driven into the earth at the bottom of the trench, generally along the back of the future curb. The string is the guide for the line (sidewise location) and grade (elevation) of the new curb. The curb may be straight and may be curved.
The next steps in the conventional method is to drive other stakes 1xc2xdxe2x80x3 behind the string line, about 5 feet apart, into the earth at the bottom of the trench. These stakes hold a back (wood) form in its vertical position such that the face of the wood is on the line of the guidance string. The wood form is usually made, for example, from 2xc3x978 (inch) and 2xc3x9712 (inch) lumber held together to form a nominal 2xe2x80x3xc3x9720xe2x80x3(actually 1xc2xdxe2x80x3xc3x9719xe2x80x3). The forms (front and back) are the mold for containing the concrete slurry which is later poured into the form. The steel curb is placed in the space between the form, against the front form.
The steel curb has a nearly vertical face, which may be about 11xe2x80x3. Two stacks of bricks are formed, spaced, for example 19 feet apart, on the bottom of the trench. The stacks of brick range in height, typically, from 10xe2x80x3 high for an 18xe2x80x3 deep curb to 19xe2x80x3-27xe2x80x3 for other curbs. The steel curb is lifted into the trench and set on the stacks of bricks. The curb has a series of protruding steel studs for anchoring the steel curb to the concrete curb. The stacks of brick are shifted so they are directly under the end studs (typically 3xe2x80x3 up and 9xe2x80x3 from each end) so they are in the position to support the curb. The stacks are inherently unstable and often topple when the curb is placed upon them. But, even if they were stable, because of the high center of gravity and a asymmetrical shape of the steel curb, the curb will not stand by itself on a stack of brick. To compensate for this when the steel curb is correctly positioned relative to the string, and while two men balance the curb, the wooden forms are placed behind and in front of the steel curb and clamped.
Each steel curb must be lifted, positioned and adjusted so that it is at the correct height relative to the guidance string. Usually wooden shims are placed on top of the stacks of bricks and beneath the steel stud for a finer adjustment. However, the conventional method described for the placement and adjustment of the steel curbs is slow, inexact and labor-intensive. The steel curb must be steadied by two men, one at each end, while 2 or 3 other men place the front and back forms and clamp them together. Wood spacers, 36xe2x80x3 apart, are positioned between the steel curbs and wood forms to keep the steel curb and wood forms from collapsing inwardly. This conventional method is expensive because of the time required, the number of men in the crew, their skill and their relatively high wages and fringe benefits.
In accordance with the present invention, to lay a line of straight steel curbs, a trench is dug and a guidance string line is positioned in the trench.
In the primary method, in accordance with the present invention, a series of sheet metal or plastic benches, one for each piece (section) of steel curb, is provided to hold and position the straight steel curb. The benches are aligned relative to the string line. The benches are raised, or lowered, by placing or removing dirt beneath their bottom plates, until the benches are at the correct elevation. Each bench has two front plates at xe2x85x9cxe2x80x3 apart, for expansion, each bracket having a support shelf to position and support the bottom edge of the steel curb. The benches are formed of sheet metal or plastic and are left in the trench after the concrete slurry has been poured. One bench supports the leading end of the previous steel curb and the trailing end of the next steel curb which is to be set. At that time, or after a series of straight curbs are positioned in the trench, wooden forms are removably placed on the benches. A wood form is positioned at the front (the side toward the road) against the lower 2-3xe2x80x3 of the face of the curb. A wood form is positioned at the back, with the form extending to the height of the top lip portion (curve-dover portion) of the curb. The concrete slurry is then poured between the form and allowed to harden. The wood forms are then removed, the trench partially filled with compacted earth and crushed stone, and the road and sidewalk are laid down.
In an alternative method, especially useful for setting curved curbs, two benches are tied to the curb, one at the leading end and one at the center. The bench and curb are then lifted by the work crew and placed in the trench in the curb""s line and grade. The trailing end of the curb is placed in the bracket of a previously positioned bench.
A corner steel curb, used at street corners and generally 85xc2x0 to 95xc2x0, is positioned in a different way. In the first step, the corner curb is lowered by the work crew into the trench and positioned on wooden blocks which lay on the floor of the trench. In the second step the tangents of the corner steel curb are aligned with intersecting streets. In the third step, metal stakes are placed in support plates welded to the curb and are driven into the ground, at the bottom of a rounded trench. The stakes are vertical. The support plates are welded to the curb. The support plate has a bushing having a bolt and the bolt is tightened on the stake to hold the curb to the desired elevation (vertical position). A series of short metal squares have been welded to the back of the curb surface towards the sidewalk in the curb fabrication shop. The squares are used in conjunction with curb ties and a series of short metal tracks. Curb ties are connected, at their front end, to the squares. At their back end, the curb ties are connected to a metal track which had been fastened, generally in the curb fabricator""s shop, fastened to a 2xc2xdxe2x80x3xc3x978xe2x80x3 or 18xe2x80x3 continuous expansion joint which separates the back of the curb from the sidewalk. The curb ties make the expansion joint, which is flexible, follow the curvature of the steel curb, and hold it in position to resist the pressure of the concrete slurry. The curb and sidewalk are poured together.